From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 673A4C43461 for ; Wed, 9 Sep 2020 10:58:20 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9231D21582 for ; Wed, 9 Sep 2020 10:58:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="tH+x30E0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9231D21582 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:References: To:From:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=EBKeDtW5IaZFO34suOzzlOo0X2Iu/x2tx+pnkoqOs3A=; b=tH+x30E0IvLQXVafjnmU8dm0s L+zYWffQzEsK8tSi5QJx/cm33qHjcXDc0ByuLMssD72Wq4KIIWY9HiNSUfKQ+E9OFKcuKeuCKCtCX yDLwfl4LU48HErwgn6Z219tlrRCJmpJlYsAcEBTWZ3ghRSgcmIU4XPkBQFIO120itjEBMEuJ7DzMS J8VpOSUh4MmPVhIql4k8+LcxWHEzpdwJahgXQmE6mGQHOHA5Aim7PTyUYYCvtWArf/dL18hCrR/ZH sYGlYfr7B44dUlkT7ak7klRIMn4bA9zJKeyVcLxtnCVoL0LLNsajjqVaqDGCUFEsbIZ8i5tlrjgud d+fSKFv4Q==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kFxmG-0002RX-4T; Wed, 09 Sep 2020 10:56:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kFxmD-0002R4-Vt for linux-arm-kernel@lists.infradead.org; Wed, 09 Sep 2020 10:56:34 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0CEB531B; Wed, 9 Sep 2020 03:56:26 -0700 (PDT) Received: from [192.168.0.110] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3CB323F68F; Wed, 9 Sep 2020 03:56:25 -0700 (PDT) Subject: Re: [PATCH v3 09/21] KVM: arm64: Convert unmap_stage2_range() to generic page-table API From: Alexandru Elisei To: Will Deacon References: <20200825093953.26493-1-will@kernel.org> <20200825093953.26493-10-will@kernel.org> <1f2e88b7-0265-195f-3bd8-4e1d5b8694e3@arm.com> <20200903175702.GA8078@willie-the-truck> Message-ID: <3aaf6f41-2a28-910b-553c-7a9e98d91165@arm.com> Date: Wed, 9 Sep 2020 11:57:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200909_065634_117542_269D6AD5 X-CRM114-Status: GOOD ( 25.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marc Zyngier , kernel-team@android.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Catalin Marinas Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Will, I'm answering my own question, again. See below. On 9/8/20 2:07 PM, Alexandru Elisei wrote: > Hi Will, > > On 9/3/20 6:57 PM, Will Deacon wrote: >> On Wed, Sep 02, 2020 at 05:23:08PM +0100, Alexandru Elisei wrote: >>> On 8/25/20 10:39 AM, Will Deacon wrote: >>>> Convert unmap_stage2_range() to use kvm_pgtable_stage2_unmap() instead >>>> of walking the page-table directly. >>>> >>>> Cc: Marc Zyngier >>>> Cc: Quentin Perret >>>> Signed-off-by: Will Deacon >>>> --- >>>> arch/arm64/kvm/mmu.c | 57 +++++++++++++++++++++++++------------------- >>>> 1 file changed, 32 insertions(+), 25 deletions(-) >>>> >>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >>>> index 704b471a48ce..751ce2462765 100644 >>>> --- a/arch/arm64/kvm/mmu.c >>>> +++ b/arch/arm64/kvm/mmu.c >>>> @@ -39,6 +39,33 @@ static bool is_iomap(unsigned long flags) >>>> return flags & KVM_S2PTE_FLAG_IS_IOMAP; >>>> } >>>> >>>> +/* >>>> + * Release kvm_mmu_lock periodically if the memory region is large. Otherwise, >>>> + * we may see kernel panics with CONFIG_DETECT_HUNG_TASK, >>>> + * CONFIG_LOCKUP_DETECTOR, CONFIG_LOCKDEP. Additionally, holding the lock too >>>> + * long will also starve other vCPUs. We have to also make sure that the page >>>> + * tables are not freed while we released the lock. >>>> + */ >>>> +#define stage2_apply_range(kvm, addr, end, fn, resched) \ >>>> +({ \ >>>> + int ret; \ >>>> + struct kvm *__kvm = (kvm); \ >>>> + bool __resched = (resched); \ >>>> + u64 next, __addr = (addr), __end = (end); \ >>>> + do { \ >>>> + struct kvm_pgtable *pgt = __kvm->arch.mmu.pgt; \ >>>> + if (!pgt) \ >>>> + break; \ >>> I'm 100% sure there's a reason why we've dropped the READ_ONCE, but it still looks >>> to me like the compiler might decide to optimize by reading pgt once at the start >>> of the loop and stashing it in a register. Would you mind explaining what I am >>> missing? >> The load always happens with the mmu_lock held, so I think it's not a >> problem because it means that the pointer is stable. >> spin_lock()/spin_unlock() imply compiler barriers. > I think you are correct, if this is supposed to always execute with kvm->mmu_lock > held, then pgt should not change between iterations. It didn't immediately occur > to me that that is the case because we check if pgt is NULL every iteration. If we > are relying on the lock being held, maybe we should move the pgt load + comparison > against NULL out of the loop? That should avoid any confusion and make the code > ever so slightly faster. > > Also, I see that in __unmap_stage2_range() we check that the mmu_lock is held, but > we don't check that at all call sites (for example, in stage2_wp_range()). I > realize this is me bikeshedding, but that looks a bit asymmetrical. Should we move > the assert_spin_locked(&kvm->mmu_lock) statement in stage2_apply_range(), since > the function assumes the pgt will remain unchanged? What do you think? What I wrote is wrong, because we can drop the lock in cond_resched_lock(). I don't see the need for any changes. Thanks, Alex _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel